Even
before “Shark Week” began last week, we all witnessed a recent feeding
frenzy of reporters all seeking “sound bites” on what has been causing
the high incidence of shark attacks off the North Carolina coast.
Unfortunately, sound bites do not lend themselves to proper public
communication of science because they are divorced from the process by
which scientists reach conclusions.

Documenting
the scientific process for reaching conclusions requires an expanded
explanation of how we scientists first erect credible hypotheses that
may reasonably explain the phenomenon, gather data to test the
hypotheses and then present the conclusions that arise from those
tests. The public interest is better served with press publication of
details of this more elaborate scientific process than with sound bites
because the publication of the entire process exposes to scrutiny the
basis on which conclusions are reached and can enrich and enliven the
public debate by showing how the data are transformed into conclusions.

Here
is what we know. In 2007, UNC-IMS faculty joined with shark experts
from Dalhousie University in Canada to publish in the journal Science a
study of temporal changes in the populations of great and small sharks
along the East Coast. A core data set analyzed in this paper was a
32-year fishery-independent sampling of sharks on the coastal shelf off
Shackleford Banks in Carteret County.

These
analyses revealed that all 11 species of great sharks sufficiently
abundant to be analyzed exhibited dramatic declines in abundance from
1972 through 2003. In contrast, of the 14 species of smaller sharks and
rays, eaten solely by these great sharks, 12 exhibited dramatic
increases up to 2003. This paper we wrote interpreted the expansion in
abundance of smaller sharks and rays to be a consequence of reduced
predation pressure from the overfished great sharks.

So
one might reasonably ask — what have the shark counts been doing since
2003? We have indeed continued this scientifically valuable shark
survey biweekly over all the warm months of each year. Over the 11
subsequent years, 2003-2014, there is no evidence of increasing numbers
of any of the 11 species of great sharks that exhibited dramatic
declines. Recovery of great shark populations in the coastal ocean off
North Carolina, then, cannot serve as an explanation for the
unexpectedly high numbers of recent shark attacks off N.C. beaches.

Some
suggest that the unusually warm weather in eastern North Carolina
during June may, along with lower gasoline prices, have led to
increased numbers of beach visitors. The hot weather may, in turn, have
motivated a higher percentage of those visitors to spend more time in
the ocean to cool off. More humans in the ocean increase chances of
shark attacks because of the increased probability of human-shark
encounters.

While
this explanation has merit, it fails to explain fully why the numbers
of shark attacks have increased in North Carolina during June as
compared to previous years. The eight shark attacks during the last
three weeks contrast dramatically with full-year totals for North
Carolina of five in 2010, four in 2011, two in 2012, one in 2013 and
four in 2014. The number of humans in the water this year has not
increased that much over the preceding years to account for this much
change in the number of shark bites alone.

One
could hypothesize that the warmer weather in June and warmer waters may
have driven great sharks further north from southern waters and into
North Carolina this year, bringing the increased risk of shark attacks
along with them. Seasonal migrations of coastal sharks are evident
along the East Coast, regularly increasing numbers of sharks off North
Carolina in early summer. This northward movement of migrating sharks
could explain the general geographic pattern of the shark attacks in
June, beginning at North Carolina’s southern beaches and then
subsequently extending to the northern Outer Banks of Dare and Hyde
counties.

Our
shark survey data for June show no indication of this suggested
temporal increase in great shark abundances, but such comparisons over
a single month (two shark sampling trips) have little power to detect
significant short-term changes in abundances. When we examine patterns
in our full 43-year survey records, shark numbers regularly peak in the
month of June.

Accounts
offered by victims and witnesses suggest that the sharks in the recent
attacks may have differed in length from 5 to 8 feet, a difference
large enough to imply that more than one individual shark, and perhaps
multiple species, were involved. Even if several sharks have been
involved in biting bathers, a single great shark is capable of
inflicting injuries to all the victims.

Satellite
tagging of several great white sharks on the East Coast over the past
few years and subsequent tracking by the Ocearch program have revealed
that these animals swim far and fast enough to have moved sequentially
from the first June attack through each subsequent one and finally
ending up off Surf City for the last attack. This is not to imply that
an individual great white shark is responsible for the all the attacks
or even for one of them. Based upon their aggressiveness towards
humans, their coastal habitats and their known propensity to chase
people at shallow wading depths, bull sharks may be the most likely
candidate for some or all attacks.

To
the degree that the northward seasonal migration of sharks explains why
June produced high numbers of shark attacks, one might suggest that
after the month of greatest risk in North Carolina has passed that we
could reasonably anticipate that shark attacks off North Carolina will
revert to very low frequencies and fade from the news headlines.

(About
the authors: Charles H. “Pete” Peterson, Stephen R. Fegley and F. Joel
Fodrie are professors and researchers at the University of North
Carolina's Institute of Marine Sciences in Morehead City.)